1. Field of the Invention
The present invention relates to a lined sleeve for tube welding and, more particularly, to a lined sleeve mounted in two tubes to be welded together to avoid failure of the tubes resulting from excessive fusion in a root of a weld or resulting from a collapse in a surface of the weld.
2. Description of the Related Art
Arc, plasma, laser beam, and electron bean are generally used to join metals together through heating. Specifically, with reference to FIG. 1, two tubes T1 and T2 to be welded together are placed end to end to form a welding zone (the adjoining zone between the tubes T1 and T2). Local heating is carried out at the welding zone to increase the temperature of the welding zone to be higher than the melting point of the tube metals T1 and T2, causing local fusion of the tubes T1 and T2. A weld 9 is formed after cooling, and a weldment is obtained.
However, excessive fusion of the weld 9 occurs easily in the hollow tubes T1 and T2 such that a large diameter difference is generated between the weld 9 and the tubes T1 and T2. In a case that the weldment is repeatedly subjected to stress, the diameter difference hinders smooth transmission of the stress and causes sharp corners between the weld 9 and the tubes T1 and T2, which results in stress concentration at the sharp corners, reduction of the fatigue strength of the weldment, and generation of cracks in the weld 9 or failure of the weld 9, shortening the service life of the weldment.
Furthermore, excessive collapses are liable to occur in the surface 92 of the weld 9 under the action of the high-temperature arc and plasma arc pressure during welding, requiring subsequent repair operation of the surface 92 of the weld 9.
Thus, a need exists for a novel lined sleeve for tube welding to avoid the disadvantages of the welding quality of the welded tubes.